1. Field of the Invention
The present invention relates to a battery pack in which a casing has an improved weld strength.
2. Description of the Related Art
A battery pack includes a plurality of cylindrical battery cells, electrode tabs for electrically connecting terminals of the battery cells arranged in a certain pattern, a lower case for containing the battery cells electrically connected through the electrode tabs, and an upper cover for covering the lower case in which the battery cells are contained, and is detachably attached to a body of an electronic apparatus, to be used as a power source for the electronic apparatus (refer to Japanese Patent Laid-Open No. 2003-257388).
In battery packs according to the related art, end parts of the lower case and the upper cover are opposed to and abutted on each other, and are welded to each other by ultrasonic welding or the like. In the battery packs according to the related art, however, the lower case and the upper cover are small in material thickness, so that the welding area between the opposed and abutted end parts of the lower case and the upper cover is narrow. Therefore, there is a problem that when an impact load generated, for example, in the case of dropping of the battery pack or the like occasion is exerted on the lower case and the upper case, the weld between the lower case and the upper cover would easily be broken (disconnected).